The structural components in hydraulic brake boosters, such as illustrated in U.S. Pat. No. 4,961,846, are designed to permit fluid under pressure in a fluid supply system to continually flow from an inlet port through a power piston to an outlet port when in an inactive or rest position. In actuation position, an input force applied to a control valve moves the control valve toward a valve seat in the power piston to restrict the flow of fluid present in an inlet chamber and create a fluid pressure differential across the power piston. After overcoming a return spring, the pressure differential acts on and moves the power piston to develop an output force. When the control valve is in the rest position, fluid freely flows through the power piston and creates essentially a broad band non-resonance sound. This broad band non-resonance sound is combined with noises produced by the engine and other components in a vehicle and is accepted as a total overall operational sound of the vehicle. When the flow of fluid through the power piston is restricted, a corresponding resonant frequency is created by the flow of fluid to the outlet port which is manifested as an undesirable noise or audible resonant sound.